Television system



14, 1937- o. B. BLACKWELL ET AL 2,101,976

TELEVISION SYSTEM Filed Sept. 18, 1929 lllllllllllll H-i-r' WQ MQQ M,

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0. B. BLACkWLL m l/E/V 70 x95 J HERMAN A TTO/P/VE Y Patented Dec. 14,1937 UNET SAiE orrics Herman, Westfield, N.

J., assignors to American Telephone and Telegraph Company, a corporationof New York Application September 18, 1929, Serial No. 393,568

14 Claims.

This invention relates to electro-optical systems and more particularlyto means for multiple channel transmission of images of still or movingobjects or of pictures.

An object of this invention is to provide an improved scanning systemand method for multiple channel operation with channels of limitedfrequency range.

Another object is to provide multi-channel image transmission in whichseveral complete images are concurrently transmitted and produce a trulycomposite image or picture.

Other objects and advantages will be apparent from the followingdescription.

In accordance with a preferred embodiment of the invention scanningmeans are provided comprising a scanning member such as a disc, having aplurality of sets of spirally arranged apertures, each set of aperturesat the transmitting station being associated with a spirally shapedphotoelectric cell. These spirally arranged apertures and theirassociated photoelectric cells for each channel have an annular lengthof approximately 360 and are interwoven or arranged in an interlockingfashion, that is, they are angularly displaced with reference to eachother by approximately 360 divided by the number of channels, thusuniformly interlocking and distributing each set of apertures withreference to each other in a symmetrical arrangement. The total numberof apertures in the scanning disc is equally divided among the severalspirals, the latter equaling the number of channels. One aperture ofeach spiral is exposed to the field of View at all times and theseapertures, due to the above mentioned angular displacement, at anyinstant are uniformly spaced apart on the field of view.

A similar scanning member or disc is used at the receiving station butinstead of spirally shaped light sensitive cells being associated witheach set of apertures, similarly shaped light sources are employed.

Electrical connection is made with the moving light sensitive cells orlight sources by means of a set of slip rings or c'ommutators connectedwith the terminals of these elements and engaging stationary brushes.

The light sensitive cells or light sources are in the form of a unitarystructure common to a plurality of apertures, preferably one for eachchannel, and as a result the Vacuum or gas pressure of these elements isthe same at all the apertures of a given channel. The chambers of all ofthe tubes may be interconnected so as to obtain uniform vacuum or gaspressure throughout and separation of the several channels maintained bythe electrical connections to separate electrodes segregated accordingto channels. If the connections with each of the light sources at thereceiving station are made through slip rings, one per channel, then thesignal current will cause generation of light throughout the whole tubefor each channel, but if the slip rings are divided into segments andeach segment connected to subdivided electrodes in the glow dischargetubes, then the generation of light may be limited to a small part ofthe light sources in the region opposite the viewing field.

It should be noted that the frequency range of each channel may belimited as desired notwithstanding the fact that each channel transmitsthe entire field for television operation. The rate at which eachchannel transmits the entire field and view is has the appearance as ifit had been transmitted over a single channel at a higher rate of k witha wide frequency range equal to the total of that of all of the channelsemployed in the multiple channel transmission.

The channels may consist of ordinary telephone circuits or open wirelines or cables, carrier telephone channels or radio channels obtainedby using different radio carrier frequencies for each channel or a radiochannel obtained by stepping up the frequency of the variousphotoelectric channels to different parts of the frequency spectrum andtransmitting the entire group of frequencies by means of a single radiocarrier fre quency.

Another arrangement for carrying out the principles of this invention inwhich the entire field of View is scanned for each channel consists ofscanning discs having quartz rods or the equivalent associated with eachof the apertures and so bent or arranged that the light is directed tostationary light sensitive cells, each cell representing a differentchannel in the transmitting station, or from stationary light sources,each light source representing a diiTerent channel in the receivingstation.

. advantage of permitting the transmitted electrical energy to be usedin small light sources, one per channel, and thus concentrate theproduction of light for each channel.

A more detailed description of the invention follows and is illustratedin the accompanying drawing.

Fig. 1 is a general schematic representation of the transmitting and thereceiving terminal apparatus connected by multiple channel transmissionlines.

Fig. 2 shows a commutating arrangement for limiting the lighted area ofthe glow discharge tubes at any instant to a small portion of theirlength, one tube only being shown. a

Fig. 3 shows a side and partial section view of the scanning disc, thespiral tubes mounted thereon and the electrical connections leadingthereto.

Fig. 4 shows an alternativechannelizing arrangement comprising means fordeflecting the light rays passing through the scanning aperturesforchannelizing the light beams.

Referring to Fig. l the scanning disc In contains three sets ofapertures arranged in the form of interwoven spirals, each spiral havingan angular length of approximately 360. The spirals are angularlydisposed with reference to each other by approximately 360 divided bythe number of channels, which in a three channel system cause adisplacement of 120. In this arrangement the spirals are uniformlyinterlocked and each set of apertures is symmetrically arranged withreference to the others. The total number of apertures in the scanningdisc is equally divided among the several spirals. One aperture of eachspiral is exposed to the field of view I6 at a time and these apertures,due to the above mentioned.

angular displacement, are at any instant uniformly spaced apart on thefield of view. Large light sensitive cells El, 22, and 213 are attachedto the scanning disc and one is associated with each set of spirals. Thecontaining vessels of these cells may be individual to each spiral orall may be interconnected so that the same vacuum exists in all, or theymay be of even smaller size than re quired for a single spiral. Oneterminal of each cell is connected to a common slip ring 30. The otherterminals of the cellsassociated with a given spiral are electricallyconnected together and to slip rings SI, 32, and 33, respectively. Theseconnections result in commoning one side of all the photoelectric cellsand grouping the other side according to channels. The common side isgrounded and the other side is connected to the respective transmissionlines by means of brushes associated with the several slip rings and theconductors ll, 52, and 43 leading respectively to the coupling elementof each transmission line. A

potential is impressed on the photoelectric cells This arrangement hasthe signal currents are amplified by means of suitable receivingamplifiers IBI, I62, and IE3 which in turn are connected to the lightsources through coupling transformers I5I, I 52, and #53 respec tivelyand the conductors Mi, I42, and I43.

The receiving scanning apparatus is similar to the transmitting scanningapparatus with the exception that light sources are employed instead oflight sensitive cells. This apparatus consists of a scanning disc IIilhaving three sets of spirally arranged apertures arranged similar tothose at the transmitting station. One aperture of each spiral isexposed to the field of View H6 at a time. Associated with each set ofapertures and fixed to the scanning disc are a plurality of lightsources. I2I, I22, and 123, each being associated with a respectivespiral of apertures and a transmission channel. 'These light sources arepreferably of the glow discharge type and the tubes associated with eachspiral, while preferably separate and not interconnected, may beinterconnected, so as to maintain uniform gas pressure throughout thusmaking all light sources operate with greater uniformity. One of theelectrodes of all light sources is connected to a common conductorleading to a slip ring I36 which in turn is connected to ground. Theother electrodes of all of the light sources are grouped according tochannels and each such group is electrically connected to slip ringsI3I, I32, and I33 of the three channels, respectively.

In the arrangement shown in Fig. 1 the received signal current of eachchannel is impressed upon the whole tube spanning all of the aperturesof a given channel thus illuminating the entire tube while the usefullight is confined to only one aperture. The illuminated area may belimited to a smaller part if the slip rings are cut into commutatorsegments and each segment connected with the electrodes associated witha few of the apertures of each spiral. Such an arrangement is shown inFig. 2, the slip rings 131, 132, and 133 being divided into commutatorsegments, a, b, c, d, ande and one set of electrodes of each lightsource spiral being divided into a corresponding number of sections A,B, C, D, and E, each of which is connected with one segment of thecommutator. The other terminals of the light sources are all connectedto the common slip ring E 38. A tube for only'one spiral and itsconnections are shown so as to avoid complicating the drawing. In thisarrangement only a small portion of the light source in any spiral isenergized and lighted at a given instant. The brushes connected with thecommutators are so positioned that the segment energized is thatconnected to the sector of the lamp opposite the viewing field or windowI5. Similar division of the light sensitive cells at the transmittingstation may be made by use of a commutating device similar to that shownin Fig. 2 if so desired.

Means for operating thescanning apparatus at the transmitting andreceiving stations in synchronism and in phase are not shown but anywell known system may be employed.

A side and partial section view of the scanning disc, the spiral tubesmounted thereon and the electrical connections leading thereto are shownin Fig. 3. While the drawing shows specifically the arrangement at thetransmitting station, the tubes being shown as light sensitive cells,the general arrangement is applicable to the receiving station requiringprimarily a change in the in terior of the tubes to convert them intoglow dis-:

charge lamps. This figure also shows an objective lens [4 for projectingan image of the objectbeing scanned at the transmitting station-upon thescanning area of the scanning disc l6 and the plate l5 containing anopening or window It bounding the scanning area. The spirally arrangedtubes 2|, 22, and 23 afiixed to the scanning disc H! are shown in crosssection and one of their electrodes is connected in common to the slipring 38 while the other electrode for each spiral or channel isindividually connected to slip rings 3i, 32, and 33 respectively.-Connection from one of these last mentioned slip rings is made to therespective transmission channels as heretofore explained in thedescription of Fig. 1.

An alternative arrangement for channelizing the light is shown in Fig.4. A scanning disc 2 it) contains a plurality of apertures arranged inthe form of spirals similar to those shown in Fig. 1 and associated witheach aperture is a quartz rod 2 l i, 2 l2, and 213 for the diiferentchannels for directing the light to one of the light sensitive cells22!, 222, and 223 or to one of the light sources associated with each ofthe respective channels at a transmitting station or a receivingstation, respectively. In place of the quartz rods, tubes havingreflecting interior surfaces, or other light directing means may beused. This arrangement permits the use of fixed light sensitive cells orfixed light sources, but it involves deflecting or bending of the lightpaths to cause channelization instead of position relation and directpassing of the light as shown in the previously described arrangement.

As heretofore stated and as shown in the drawing, one aperture of eachspiral is in front of the viewing field or window at all times and thelight passing through each of these apertures is associated with adifferent channel. Also these apertures are preferably so angularlypositioned that they travel across the field with a uniform spacing,although the more important feature is that of uniform radial separationat all positions so that as the first third of the apertures of a givenspiral is scanning the top third of the field the second third of thesecond spiral is scanning the second third of the field and the lastthird of the third spiral is scanning the last third of the field, andso on. Each third of the field is scanned at a rate which is within thetime of the persistence of vision. In the second third of a revolutionof the scanning disc each spiral is scanning the next third of the fieldand in the last third of a revolution, each spiral is scanning thesucceeding third of the field. This results in each channel scanning andtransmitting image currents of the entire field with the result thateach channel transmits a complete image which at the receiving stationis superimposed upon that of the images transmitted by the otherchannels and a truly composite picture produced. The rate of rotation ofthe scanning disc is cut down, compared with a single channel system, inproportion to the number of channels simultaneously employed. In thethree-channel system the rate of rotation is one-third that requiredfora single channel system. The same results are obtainable from thescanning arrangements shown in either Fig. 1 or Fig. 4.

What is claimed is: v

1. The method of limiting the frequency range required for each channelin multi-channel electro-optical transmission which comprisesconcurrently and repeatedly scanning the entire area of the same fieldof view for the different channels, a scanning of a given elemental areafor each channel taking place later than a scanning of that area for adilferent channel by a period approximately equal to each scanningperiod divided by the number of channels.

2. The method of 'multi-channel television which comprises concurrentlyand repeatedly scanning the entire area of the same field of view forthe different channels, a scanning of a given elemental'area for eachchannel taking place at a period later than ascanning of that area for adifferent channel by r a period approximately equal to that of thepersistence of vision.

3. A television system comprising a plurality of transmission channelsand means associated with each channel for repeatedly concurrentlyscanning the field of View and for causing a scanning of a givenelemental area for one channel to take place at a time later than thatof an elemental area in the same region of the field for another channelby a period approximately equal to the period of persistance of vision.

4. A multiple channel electro-optical system comprising an aperturedscanning disc having a plurality of sets of spirally arranged aperturesand a spirally shaped light sensitive element associated with each of,said sets of spirally arranged apertures arranged in interlockingpositions and having in operation a phase displacement equal to acomplete individual scanning cycle divided by the number of said sets ofspiral- 1y arranged apertures.

5. A rotatable apertured scanning element having a row of spacedapertures and a single photoelectric cell conforming to the shape ofsaid row of apertures and means for rotating said cell in fixed relationwith said scanning element.

6. A rotatable scanning element having a plurality of overlapping rowsof apertures, a corresponding plurality of elongated photoelectric cellseach conforming in shape to one of said rows of apertures andcooperating therewith and means for rotating said cells in fixedrelationwith said scanning element.

7. The method of producing a television image which comprises producinga plurality of similarly placed images of the same field of view, eachimage being produced in a period greater than that of the persistence ofvision and the production of said images being overlapping in time.

8. A multiple channel electrooptical system comprising an aperturedscanning disc having a plurality of sets of spirally arranged aperturesand spirally shaped lamps associated with said sets of spirally arrangedapertures respectively to move therewith.

9. A television image producing system comprising a rotatable scanningelement, a plurality of spirally shaped lamps attached thereto androtating therewith, and means for continuously connecting each of saidlamps to a respective input circuit.

10. Television scanning means comprising a rotatable member, a pluralityof tubular lamps each of length many times its greatest transversedimension, means for fixedly associating said lamps to said rotatableelement with the longitudinal axes of said lamps lying along parallelcurved lines, and means in part stationary and in part movable forconducting image currents to said lamps.

11. Television scanning apparatus including a spiral photo-electrictube, means for rotating said tube about its axis, and means forscreening all of said tube at any instant except a single elementalscanning area thereof.

12. Television scanning apparatus including an electro-opticaltranslation device arranged in the shape of a spiral tube,'means forrotating said tube about its axis, and means for screening all of saidtube at any instant except a single elemental scanning area thereof.

13. Image producing means comprising a series of strip light sources,and means for simultaneously energizing a plurality of said lightsources to constitute remotely spaced unit lines of the image and forsuccessively energizing all of said sources. 7

OTIO B. BLACK'WELL. JOSEPH HERMAN.

